For operation with a two-phase refrigerating medium, suitable cooling systems are known from DE 10 2006 005 035 B3 and DE 10 2009 011 797 A1, and are used, for example, to cool food which is stored on board a passenger aircraft and intended to be given out to the passengers. Typically, the food which is provided to supply the passengers is kept in mobile transport containers. These transport containers are filled outside the aircraft, precooled, and after being loaded into the aircraft put into appropriate positions in the aircraft passenger cabin, e.g. the on-board kitchens. To ensure that the food remains fresh until it is given out to the passengers, cooling stations, which are supplied with cooling energy from a central cold-generating device and deliver this cooling energy to the transport containers with the food stored in them, are provided in the region of the transport container positions.
Compared with cold-generating units in the form of units at the individual transport container positions, a cooling system with a central cold-generating device has the advantages of a smaller installed volume and lower weight, and also costs less to assemble and maintain. Also, if a cooling system with a central cold-generating device which is arranged outside the passenger cabin is used, machine noises which are generated by cold-generating units placed in the region of the transport container positions, and which are audible in the passenger cabin and can thus be experienced as disturbing, can be avoided.
In the case of the cooling systems which are known from DE 10 2006 005 035 B3 and DE 10 2009 011 797 A1, the phase transitions of the refrigerating medium which flows through the cooling circuit of the cooling systems, said phase transitions occurring in operation of the system, make it possible to use the occurring latent heat consumption for cooling purposes. The refrigerating medium mass flow which is required to provide a desired cooling power is therefore significantly less than in, for example, a liquid cooling system in which a single-phase liquid refrigerating medium is used. Consequently, the cooling systems which are described in DE 10 2006 005 035 B3 and DE 10 2009 011 797 A1 can have smaller conduit cross-sections than a liquid cooling system with comparable cooling power. The reduction of the refrigerating medium mass flow also makes it possible to reduce the conveying power which is required to convey the refrigerating medium through the cooling circuit of the cooling system. The result of this is increased efficiency of the system, since less energy is necessary to operate a corresponding conveying device, e.g. a pump, and also less additional heat, which is generated by the conveying device in operation of the conveying device, must be carried away from the cooling system.
In the case of the cooling systems which are known from the prior art, the two-phase refrigerating medium is usually stored temporarily in the form of a boiling liquid, in accumulator vessels which are integrated into the cooling circuits of the cooling systems. To prevent the refrigerating medium evaporating when it is sucked through a conveying device, e.g. in the form of a pump, it is therefore necessary to subcool the refrigerating medium which is stored temporarily in the accumulator vessels correspondingly. This is usually done by a pressure increase, which is achieved by a suction nozzle of the conveying device being arranged in a defined position below a sump of the accumulator vessel, from which the refrigerating medium which is stored temporarily in the accumulator vessel is discharged from the accumulator vessel. In other words, the conveying device is positioned relative to the accumulator vessel in such a way that for the conveying device a positive minimum inflow level, which is defined by the height of a liquid column over a leading edge of a rotating blade of the conveying device, is maintained. The gravitational force of the liquid column causes a defined pressure increase in the refrigerating medium which is fed into the conveying device, and in this way ensures subcooling of the refrigerating medium, and prevents evaporation of the refrigerating medium.
However, when a cooling system is fitted in an aircraft, the problem often occurs that it is difficult to house the system components in the very restricted installation space, or even, as described above, to position them relative to each other in such a way that, for example, by exploiting the gravitational force of a liquid column over a leading edge of a rotating blade of a conveying device a pressure increase in the refrigerating medium which is fed to the conveying device can be achieved, and thus evaporation of the refrigerating medium because of a pressure reduction caused by the conveying device can be prevented.